Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $13.69   7.370%   $14.699   $14.70   $14.70   $14.70  
  Purchase #2 $188.37   8.684%   $204.7281   $204.73   $204.75   $204.70  
  Purchase #3 $166.56   12.319%   $187.0785   $187.08   $187.10   $187.10  
  Purchase #4 $38.67   12.591%   $43.5389   $43.54   $43.55   $43.50  
  Purchase #5 $68.73   8.265%   $74.4105   $74.41   $74.40   $74.40  
  Purchase #6 $62.60   3.622%   $64.8674   $64.87   $64.85   $64.90  
  Purchase #7 $242.43   8.277%   $262.4959   $262.50   $262.50   $262.50  
  7 purchase totals = $781.05       $851.8183   $851.83   $851.85   $851.80